This relates to apparatus for generating high frequency harmonic signals and, more particularly, to frequency multipliers using a semiconductor diode with a nonlinear capacitance-voltage characteristic.
Frequency multipliers, or harmonic generators, employing nonlinear semiconductor devices such as varactors or step recovery diodes are well known. For example, an impulse circuit utilizing a step recovery diode is disclosd in U.S. Pat. No. 3,374,416 to R. D. Hall et al issued Mar. 19, 1968. Frequency multipliers with step recovery diodes have proven to be superior to those with varactors particularly in applications requiring high output-frequency/input-frequency ratios also known as high order multiplication. Desirable characteristics of frequency multipliers include stability, high efficiency, broadband operation for versatility, and a smooth, pure sinusoidal output waveform.
Conventional step recovery diode frequency multipliers have provided satisfactory performance for most applications when operated at a relatively low bias mode. In this mode, the step recovery diode produces one pulse per period of the input signal by switching into a nonconductive state. In a paper entitled "Simulation of High-Order, Charge-Storage-Diode Multiplier on an Analog Computer" by P. W. C. Chilvers and K. Foster in Electronics Letters, Vol. 3, No. 6, June 1967, pp. 277-278, step recovery diode operation in harmonic generators is described to provide a better understanding of the operation and design criteria for these circuits.
Variation of an external dc bias to an appropriate level for the step recovery diode, as mentioned in the aforementioned paper, produced a spurious mode of operation wherein multiple transitions occurred within one period of the input signal. However, this mode of operation was also characterized as being undesirable primarily because of instability and also low efficiency. It was then pointed out that the point of best efficiency was just before the point of double transition.
It is a primary object of this invention to provide a highly stable and versatile frequency multiplier by using a step recovery diode to produce multiple transitions during each period of the exciting input signal.
It is a related object to provide a high impedance environment for the pulse generating circuitry of the step recovery diode to reflect energy back to the diode for efficient and stable operation of a high order frequency multiplier.
It is another object of this invention to provide a relatively simple circuit arrangement for a high order multiplier with minimal manufacturing and tuning adjustments.